Multiple station turret punch machines provide a plurality of different punch stations for use in conjunction with a like number of opposing die cavities. Each station includes a punch unit and a corresponding die. Typically, several punch and die combinations are used in sequence to suitably shape a workpiece.
The punch machines generally have either a hydraulic ram or a mechanical ram for driving the punch downwardly against a workpiece. Punch machines having a hydraulic ram use a hydraulic fluid and drive cylinder system to reciprocate the ram upwardly and downwardly. In hydraulic ram punch presses, the ram may be sustained in any position along the stroke of the drive cylinder by appropriately controlling the amount and pressure of the hydraulic fluid in the drive cylinder. One such hydraulic ram punch press is the Amada Vipros 357. In punch presses having a mechanical ram, a cam-like head is mounted on a rotating shaft which is positioned substantially normal to the axial movement of the punch to reciprocate the ram. The cam-like head momentarily strikes the punch unit on its downward stroke, and then returns to its raised position as the shaft is rotated. One such mechanical punch press known in the art is the Amada Lyla Series 50-50-72.
Conventional punch units have a punch guide, a punch driver, and a punch tip fixedly attached to the punch driver. The punch driver and punch tip are positioned in the punch guide for reciprocal axial movement along the longitudinal axis of the punch guide, and the guide itself is positioned within a tool-receiving aperture in a turret for reciprocal axial movement therein, all in a manner known to the art. Punch tips may have a variety of shapes for punching holes, cutting, and making impressions in a workpiece.
Conventional dies mate with conventional punch units. A die is fixedly positioned underneath a mating punch and receives the punch tip as it punches through a workpiece. The punch tip may have a cutting face of any desired shape, and the mating die may have a correspondingly shaped orifice so that holes of the desired shape are formed in the workpiece. If a dimple is to be formed in the workpiece, the punch may have a generally spherical convex workpiece contacting face, and the die may have a correspondingly shaped concave surface.
In general, a turret punch press includes a horizontal workpiece support surface and a mechanism for moving a workpiece in a precise and predetermined manner on the support surface. The punch press includes a punch station where the punching operation occurs, generally in the plane of the support surface. The press also includes a turret that rotates about a vertical axis. Aligned, tool-receiving frames are carded by the turret on each side of the plane of the workpiece support surface. The upper frame usually holds a series of punches spaced circumferentially around the frame, and the lower frame holds a series of circumferentially spaced dies aligned beneath and mated to the respective punches. The punches are spring-biased upwardly and are mounted to move from their upper positions downwardly into lower, punching positions when struck by a punch press ram.
In a typical punching operation, a workpiece is clamped in a desired position on the support surface and the turret is rotated to bring a selected punch and die combination to the punch station. The punch ram is then cycled downwardly and upwardly, striking the punch on its downward stroke to drive the punch tip into a workpiece-deforming position in which the punch tip contacts the workpiece.
An elongated rib may be formed in a workpiece by making a series of dimples, moving the workpiece slightly between each dimple. Forming elongated deformations of this type using conventional punch tools is time consuming and produces excessive wear on the equipment. To create a deformation larger than the cross-section of the punch tip, the workpiece must be incrementally moved between punching operations. In fast punch presses, the ram can reciprocate several times per second. However, to create a smooth deformation in nibbling or rib-forming operations, a workpiece typically can only be moved about 1/32" after every stroke of the ram. Conventional punch tools thus may be able to form a rib at a rate of only about 1/8 inch per second. This rate of deformation prevents cost effective use of punch presses to machine curved deformations such as the raised ribs on metallic cylinder gaskets.
Additionally, when conventional punch units are so used, they tend to create small, unintentional but visible marks in elongated ribs or other impressions. The unintentional marks are roughly transverse to the longitudinal direction of the ribs so that they reduce the quality of the resulting product.
In light of the problems of conventional punch units, the present inventors developed a punch and die assembly with rollers for use in hydraulic punch presses. The device requires punch presses in which the ram can maintain continuous pressure against the punch tool while the punch is in the depressed position. Accordingly, the device is generally limited for use in hydraulic punch presses.
As previously described, however, many punch presses have mechanical rams that reciprocate upwardly almost immediately after the punch unit reaches the depressed position. Since mechanical rams cannot maintain the continuous pressure necessary to operate the roller punch and die assembly designed for hydraulic punch presses, a need exists to provide another roller punch and die assembly that is self-locking in the depressed position and self-releasing from the depressed position for use in mechanical punch presses.